1. Field of the Invention
The present invention relates to a physical sensor and a method of producing the same and is suitable for, in particular, physical sensors such as a pressure sensor, an acceleration sensor and yaw rate sensor and the method of producing the same.
2. Description of the Related Art
As a conventional physical sensor, there have been known a pressure sensor, an acceleration sensor and yaw rate sensor described in Japanese Patent Application Publication No. 2004-255562. The physical sensor includes a semiconductor substrate, an insulating film formed on the semiconductor substrate, a structural layer formed on the insulating film, a glass substrate anodically bonded to the structural layer while a vacuum chamber for protecting the structure of the structural layer is being formed, a via hole in the glass substrate formed in a position corresponding to the underbump metal of the structural layer and a solder ball which is provided for the via hole and coupled with the underbump metal to capture a detected signal.
In the physical sensor described in the above JP 2004-255562, the via hole is formed in the glass substrate. There have been available, roughly speaking, three methods for processing the via hole in the glass substrate: first for processing using chemical reaction; second for processing using laser processing; and third for processing using machining.
Firstly, processing using chemical reaction, which is the first processing method, is described below. Wet etching using a solvent and dry etching using gas apply to the processing using chemical reaction. The above processing has an advantage in that the formation of a mask enables collectively patterning a pattern. For a glass processing, however, a hole is enlarged because it is difficult to use the difference between wet etching rates due to a difference in crystal orientation. Dry etching is capable of processing a hole with a narrow gap depending on the selection of conditions, however, it takes several times to several tens of times as long as other processing.
Secondly, processing using laser processing, which is the second processing method, includes excimer laser processing and CO2 laser processing. The bore diameter of laser processing is determined by a spot diameter, enabling narrow-gap processing. However, the laser processing processes holes one by one, which increases the number of holes to takes a long time to process. Recently a wafer level package has prevailed, a wafer increases in diameter and the number of processed holes required for one wafer tends to increase.
Thirdly, processing using machining, which is the third processing method, is described. The machining includes drilling and sand blasting. The drilling is capable of forming a hole perpendicular to a wafer surface, however, it is necessary for the drilling to process holes one by one, as is the case with the laser processing. The sand blasting allows holes in a wafer to be simultaneously processed. However, it is substantially impossible for the sand blasting to process a narrow-gap hole due to the problems in that a processed wall is tapered, chippings are produced on the side where processing is omitted and a processed surface is easily cracked.
As described above, it is therefore difficult for the above methods to process a narrow gap in the glass substrate without spending a long time, which bottlenecks the miniaturization and high density of a physical sensor and high density.